1. Field of the Invention
The present invention relates to a curable composition. In particular, the present invention relates to a curable composition, which is suitable for use as the packaging material of electronic components such as light emitting diodes.
2. Descriptions of the Related Art
Organic resin, due to its properties of high processability, light weight, low cost and impact resistance etc., has gradually replaced inorganic glass for use as optical components such as optical lens and packaging materials of electronic components. Recently, due to the development of light emitting diode techniques (e.g., high brightness, multiple color property etc.), organic silicon resins which have better heat resistance, water resistance and transparency, have gradually replaced epoxy resins for use as the packaging material of electronic components.
An organic silicon resin, such as organopolysiloxane, can be cured through alkylation with silicon hydrides. The cured solid product of the alkylation has a high refractive index and transmittance, and can be used as the packaging material of a light emitting diode. For example, JP H8-176447 discloses a curable organopolysiloxane composition, comprising an organopolysiloxane in which each molecule has a silicon-bonded phenyl group and an silicon-bonded alkenyl group, an organic hydrogen siloxane, and an addition catalyst; and JP 2003-128922 discloses a curable organopolysiloxane composition, comprising an organopolysiloxane in which each molecule has at least two silicon-bonded alkenyl groups and a silicon-bonded phenyl group, an organopolysiloxane in which each molecule has at least two silicon-bonded H, and an addition catalyst. Such curable organopolysiloxane compositions, due to their high viscosities, have disadvantages including operation difficulty and poor adhesive property to the substrate.
U.S. Pat. No. 7,527,871 B2 discloses a modified curable organopolysiloxane composition, in comparison to the above prior arts, which comprises a component of a linear organopolysiloxane with at least two silicon-bonded alkenyl groups and at least one aryl group and thus, can provide a cured product with a low viscosity and well adhesive property. However, during the synthesis of the above component, a great amount of nonreactive residue of methyl phenyl rings is inevitably generated for the reaction equilibrium, which will make the surface of the cured product obtained from the composition sticky. In addition, any procedure used to remove the rings, such as a high-temperature distillation, will probably lead to the breakage of the bonding between the phenyl groups and result in the appearance of yellowing. Furthermore, since the added component is a linear organopolysiloxane with insufficient strength, the cured product will tend to fracture under a high temperature or a drastic temperature variation.
In general, to achieve higher transmittance and superior water resistance and gas resistance, the packaging industry tends to adjust the content of the aromatic groups so as to increase the refractive index (i.e. >1.5) of packaging materials. However, the increase of the refractive index results in poor heat resistance of the packaging materials such that the packaging materials will yellow when exposed to high temperature. Therefore, such packaging materials are not suitable for high-power semiconductor devices. If the packaging materials are adjusted to have a lower refractive index (i.e. <1.43), although the heat resistance of the packaging materials can be improved, the water resistance and gas resistance will be decreased and transmittance will also be sacrificed. Accordingly, a packaging material simultaneously having high transmittance, superior water resistance and gas resistance and improved heat resistance is in high demand in the industry.
In view of the above, the present invention provides a curable composition without any undesired residue of rings produced during the manufacturing process. The cured product of the composition has outstanding heat resistance, transmittance, water resistance and gas resistance, and barely yellows when exposed to high temperature. In addition, the ratio or structure of the components contained in the curable composition can be adjusted to satisfy the demands of a quick curing process and to provide the desired properties including superior transmittance, heat resistance, water resistance, gas resistance and surface conditions.